Foamed and cross-linked phenolic resin and method for making same

ABSTRACT

A phenolic foam having exceptional absorption capacities for pollutants such as hydrocarbons and other substances is described. The foam is hydrophobic and is capable of absorbing such substances in amounts up to 72 times its own weight. It is the reaction product of a resol and a cross-linking agent made of linear and/or cyclic, partially or completely sulphonated, phenolic oligomers, in the presence a surfactant and a swelling agent, and, optionally, of a coloring agent and stabilizers. A method for making the foam, an installation for implementing the method and a use of said foam are also described.

The present invention belongs to the field of cross-linked phenolicresins. In particular, it is related to a new cross-linked phenolicresin in the form of a foam, and to a process for the preparation ofthis foamed cross-linked phenolic resin having special surface activeproperties. The invention is further related to an installation for themanufacture of the phenolic foam.

Accidental pollution of water provoked by hydrocarbons on the sea and onland and touching the sea, the coasts and inshore waters have becomemore and more frequent and constitute a very serious problem to theenvironment. The means available for confining the pollution and forcollecting the spilt hydrocarbons are limited. In spite of all searchefforts that have been made, it has not been possible to find a meanssimple to apply, having a safe and reliable action and being furthermoreinexpensive and easy to collect. For example, it has been tried torender the spilt hydrocarbons wettable by spreading surface activeagents onto the surface of polluted water in order to obtain an aqueousdispersion, but this method brings about risks of toxicity and does noteliminate the hydrocarbons themselves. Undoubtedly, the best methodcomprises the removal of the hydrocarbons from the water by absorptionor adsorption by means of solid bodies that are much easier to separatefrom the contaminated surface and to be removed therefrom.

It has therefore been suggested to use, for example, the followingabsorbing materials: pre-treated minerals such as perlite and bentonite;fibrous materials such as cellulosic fibers, glass fibers and peat;synthetic materials, e.g. polyurethane, polyethylene, polypropylene,epoxy resins, polyesters, and also urea formaldehyde resins. Among thesematerials, hydrophobic products should be preferred since they have abetter absorption power; for example, microporous polypropylene has anabsorption power that is 23 times its weight whereas the peat, ahydrophilic matter, absorbs only 8.3 times its weight of hydrocarbons.

According to French patent No. 2,073,083, one has already suggested touse a phenolic foam for the fixation of oils, fats, petrol (gasoline)and similar products spilt on the surface of solids or liquids, forexample on water. However, this document fails to mention data regardingthe composition of the foam excepted that it is a foamed phenolic orformol-phenolic resin, and regarding the properties of the foam. As itwill be shown below, the phenolic foams known until now are not veryeffective for the absorption of fatty materials in view of theirhydrophilicity.

Therefore, there is a strong need of a new, more effective absorbingmaterial which can be used to combat the pollution of the environment byhydrocarbons.

The object of the present invention is therefore to provide a newabsorbing, lipophilic material which can be used especially as anantipollution material.

This objective is attained by the phenolic foam according to thisinvention that is defined in the first independent patent claim. Thesecond independent patent claim is directed to a manufacturing processof the new foam, and the third independent patent claim to aninstallation for carrying out the process. The fourth independent patentclaim finally defines a use of the foam. The subject of the dependentpatent claims are special embodiments of the subject of theirsuperordinated independent claims.

In order to obtain the foam of the invention, it is necessary to combinein a new and unexpected manner at least the following components:

a reactive phenolic resin, preferably of the resol type;

a surface active agent, preferably of the polyetherpolysiloxane type ora polyether, modified by a dimethylpolysiloxane copolymer;

a cross-linking agent selected from sulfonated phenolic oligomers; and

a blowing or foaming agent.

Other component may additionally be present, preferably one or morecoloring agents and stabilizers.

In the following, these components will be described in more detail.

The resol

It is known to manufacture phenol-formol oligomers and to condense samein the presence of acidic catalysts. These oligomers, called resols, areprepared from optionally substituted phenols and formaldehyde in aqueoussolution, using specially selected stoichiometric ratios and a basiccatalyst. The resols show a tendency to a slow polycondensation; thispolycondensation can be accelerated by an acidic catalyst, generallysulfuric acid which however remains as such within the phenolic plasticobtained after the polycondensation of the resol.

It has already become known to manufacture phenolic foams by apolycondensation of still liquid phenolic resins in the presence of ablowing agent, this polycondensation being effected by the action of anacidic catalyst that does not take part as a cross-linking agent in thechemical reactions. Such foams are useful as heat and noise insulatingmaterials. However, the disadvantages of these foams are also based uponthe presence of a strong free acid which cannot be removed by washingsince it is imprisoned within the macromolecules of the phenolicplastic. Furthermore, these foams are hydrophilic.

The surface active agent

The surface active agent is specially selected for producing thecellular structure of the hydrophobic foam to be manufactured, on onehand, and for imparting the hydrophobicity to the foam, on the otherhand. It is generally introduced into the resol during the manufactureof the resin. The non-ionic and amphoteric surface active agents do notmodify the shelf live of the resols and are thus preferably used.

The surface active agents which will be used in the frame of the presentinvention should be water soluble and have an HLB value (hydrophiliclipophilic balance) of ≧10, and they should be stable in the presence ofstrong acids constituted by the cross-linking agent (sulfonic acids).

The use of ethylene and propylene oxide copolymers and in particular ofdifferent organo-silicon compounds, of polydimethyl siloxanes, and ofpolysiloxane polyether copolymers and polysiloxane polyglycols ispreferred. As examples, silicone glycol copolymers and polysiloxanepolyether copolymers are cited. However, these classes of surface activeagents are examples only.

The cross-linking agent

According to the present invention, it has been found that certainsubstances having an acidic character can advantageously replace theacid catalysts such as sulfuric acid that are at present used for thecondensation of resols. It has been found that these substances whichare proposed by the invention for the replacement of the acid catalystare constituted by partially or totally sulfonated phenolic oligomers.These substances are exactly of the same nature as the resols with theexception of their --SO₃ H substituents, and they are chemicallycombined with the resols and form the bridges between the resolmolecules; they are thus not physically imprisoned within the phenolicplastic network under formation but are incorporated into this networkas a chemical constituent thereof.

The invention uses the new cross-linking agent in the form of partiallyor completely sulfonated linear phenolic oligomers, of sulfonatedphenol, of partially or completely sulfonated cyclic phenolic oligomers,or of mixtures thereof, and each mixture may further contain simplesulfonated phenol. The diversity of these cross-linking agents confersto the phenolic foam according to this invention its special properties,namely one may adjust the final properties of the foam to bemanufactured by an adequate selection of the cross-linking agent.

Sulfonated cyclic phenolic oligomers are in part already known; however,they have never been proposed yet as an additive to resols for theirpolycondensation. Sulfonated cyclic phenolic oligomers have for examplebeen disclosed in the article "Synthesis and acid-base properties ofcalix 4!, calix 6! and calix 8!arene p-sulfonic acids" by J. P. Scharff,M. Mahjoubi and R. Perrin, New J. Chem. 1991, 15, 883-887 but their useaccording to the invention, namely as a cross-linking agent, has notbeen suggested nor disclosed.

The blowing agent

This product is incorporated into the foam forming mass is in order toform the pores. The blowing agents should be

compatible with the surface active agents,

uninflammable, having no flash point,

a low boiling point, i.e. <35° C.,

a low heat of vaporization, namely <300 kJ/kg.

They may be selected from the families of hydrocarbons HC, thechlorofluorocarbons CFC, the hydrochlorofluorocarbons HCFC or thehydrofluoroalkanes HFA, and from the mixtures of substances selectedfrom these classes. One example is the HCFC 141.

Additives

Certain additives may be added to the starting formulation of the foam.In particular, coloring agents are to be mentioned but other additivesare also contemplated, namely stabilizers, for example antioxidants andanti-UV agents. The coloring agent serves to give the foam an aspectdistinguishing it from other product and for following the absorptionprocess during its use.

Depending on the applications and uses of the foams of the invention,coloring agents are necessary. Azoic coloring agents or dyestuffs are tobe mentioned, preferably phenolic azo dyes.

Sulfonated phenolic azo dyes have the advantage that they canimmediately be used in the cross-linking system; they are stable inacidic mediums, show antioxidant properties, and supply a supplementaryacidity to the cross-linking system.

The dyestuffs that are generally introduced in an amount of from 0.1 to1% by weight of the cross-linking agent are monomers such as those ofthe formula ##STR1## or azoic cyclic oligomers of the family of coloringcalixarenes.

The preferred manufacturing process for the absorbing foam is generallycarried out in the following manner:

1. Preparation of the resol

The preparation is generally carried out according to the already knowntechniques: The components, namely the phenol, the formaldehyde sourceand the alkaline catalyst, are charged into a reactor in the desiredratios, the mixture is reacted under stirring and under precise andcontrolled temperature conditions, the reaction mixture is then allowedto ripen during a predetermined time duration, and the resol is finallyrecovered for subsequent use. The resol component contains preferablythe surface active agent which is added to the resol after or during theripening step.

2. Preparation of the cross-linking agent

The cross-linking agent is prepared from optionally substituted phenol,an acidic catalyst, and a formaldehyde source, the oligomers thusobtained are then more or less sulfonated, and the cross-linking agentis then recovered and stored for a subsequent use. If it is desired thatthe cross-linking agent contains sulfonated cyclic phenolic oligomers,it is preferred that such oligomers not yet sulfonated are separatelyprepared, that they are sulfonated, and that these are added to theabove reaction mixtures prior to their storage

Foam

The manufacture of the foam uses the different components describedabove. The process is designed as a continuous one. The resol (preparedaccording to the technique described above), the cross-linking agent(see also the above preparation step) and the blowing agent are meteredin the predetermined ratios into a mixer device. The mixer produces anintimate blend of the introduced components, and the expansion isautomatically initiated since the cross-linking reaction of the resol isexothermic, resulting in a temperature increase of the mixture beyondthe boiling or decomposition temperature of the blowing agent,respectively, for example 80° C.; this temperature depends of course onthe type of the blowing agent and the selected reagents. In this manner,the exothermicity of the cross-linking reaction is used to bring aboutthe evaporation of the blowing agent.

The cross-linking of the resol under expansion and the solidification ofthe formed foam are accomplished on a casting belt continuously runningunder a delivery head of the mixer device. The reaction mixture is thuspoured on the running belt which may be temperature controlled, in theform of a pouring that expands during a few seconds and forms a solidfoam string at the end of the running belt. This string is then shreddedinto pieces of different desired size and shape. For example, accordingto the mechanical speed of the selected shredder device, it is possibleto produce foam pieces of about 5 to 5 cm, useful for combatingpollution, or flakes or pieces of any other size if desired.

The installation for the manufacture of the foam according to theinvention comprises the following units:

a resol production unit, comprising a reactor equipped with a stirrer, athermostated double shell, and the recipients and tanks necessary forthe starting materials: phenol, sodium hydroxide solution,paraformaldehyde, and the conventional metering and transportationdevices. This unit further comprises ripening reactors for carrying outthe final reaction, these ripening devices being equipped with atemperature control, and a storage tank;

a unit for the production of the sulfonated cross-linking agent,comprising, for each constituent of the mixture that forms thecross-linking agent, at least one reactor equipped with a stirrer, athermostated double shell, and the recipients and tanks necessary forthe starting materials: phenol, sulfuric acid, formaline, water andoptionally other additives such as cyclic phenolic oligomers. This unitfurther comprises mixing tanks for blending the different constituentsof the cross-linking agent as well as storage tanks and the conventionalauxiliary devices;

a foam production unit, comprising supply pumps, a mixer device equippedwith supply tanks for the resin that contains the surface active agent,for the cross-linking agent and the blowing agent as well as the weightor volume metering devices, and a casting belt or similar;

a shredder and storing unit; and

optionally, a conditioning and/or packaging unit.

The invention will now be described in more detail in making referenceto the drawing showing an example of the installation, and in givingexamples of the manufacture itself.

The attached drawing shows the different units described above, namely:

FIG. 1 is a schematical representation of a resol manufacturing unit;

FIG. 2 is a schematical representation of a manufacturing unit for thecross-linking agent comprising sulfonation;

FIG. 3A is a schematical side view of a foam production unit; and

FIG. 3B is the continuation to the right of the unit according to FIG.3A that also shows a shredder unit for the foam containing a storagedevice.

The Figures could be drafted as a schema since the different elements ofthe units are typically apparatuses and devices that are known per se;furthermore, auxiliary devices and members such as thermometers, pumps,elements and members for regulation and control, supply devices forelectric current and other energies are not shown either since they arewell known to the one skilled in the art.

FIG. 1 shows schematically the resol manufacturing unit. The materialsand substances that are to be reacted are stored in tanks 10 to 16. Tank10 contains phenol, typically containing about 10% by weight of water inorder to keep it easier in the liquid state; tank 10 is equipped with athermal insulation, a heat exchanger, and a constant feed motor pump(these elements are not shown). Tank 12 is to contain an aqueoussolution of caustic soda (NaOH); it is made of special steel. Tank 14simply contains water, and tank 16 is a silo for the paraformaldehydecomprising a delivery device, an installation for maintaining itscontent under nitrogen, a vibrating device on the tank and a deliveryscrew with a delivery speed control.

The four storage tanks 10 to 16 are connected by ducts 18, 20, 22 and24, respectively, to reactor 26 which is equipped with a stirrer, adouble shell for receiving a temperature controlled fluid, and athermometric sensor.

The unity according to FIG. 1 additionally comprises at least onereactor for completing the principal reaction; these reactor are called"ripeners"; in FIG. 1, three ripeners 28, 30 and 32 are shown that areconnected by conduits 34 to the discharge outlet of the reactor 26.Furthermore, it is possible to add a stabilizer, stored in tank 36, andalso, if this is desired already in this stage of the process, thesurface active agent from tank 38 into the ripeners. The conduits 40 and42 connect tanks 36 and 38, respectively, to the ripeners 28, 30 and 32.The ripeners are equipped with a temperature controlled double shell anda stirrer. The discharge outlet of each ripener is connected by a duct44, 46 and 48, respectively, to a large storage tank 50 for the resol.

FIG. 2 shows a principal flowsheet of the manufacture of the linear andcyclic sulfonated phenolic monomeric and oligomeric cross-linking agentsas well as of sulfonated phenol. A Grignard type reactor 52 has acapacity of 1250 liters; it is constructed from stainless steel with adouble shell and with an insulation. This reactor 52 comprises also astirrer, an ascending condenser and a thermometric sensor. Reactor 52 isconnected by conduits 53, 55 and 57, respectively, to a tank 54 thatcontains phenol, a tank 56 containing formaline (an aqueous formaldehydesolution), and a tank 58 containing sulfuric acid. A conduit 60 permitsto remove condensed water during the reaction and to supply it to astorage vessel 62.

A second reactor 64, identical with reactor 52, is provided for thepreparation of sulfonated phenol. It is connected via ducts 65, 67 and69, respectively, to a phenol tank 66, a sulfuric acid tank 68, and awater tank 70.

Conduits 72 and 74 lead from reactors 52 and 64, respectively, to aripening and mixing vessel 76 of the type already described inconnection with FIG. 1. The mixing ratio of the products discharged fromreactors 52 and 64 can be adjusted by adjusting the amounts passingthrough conduits 72 and 74. A tank 78 contains sulfonated cyclicphenolic oligomers, and it is possible to transfer, if desired, theseproducts into the ripener 76. The cross-linking mixture is then emptiedinto the storage tank 80.

FIGS. 3A and 3B schematically show a flowsheet of the manufacturing ofthe foam starting from the components mentioned above. The cross-linkingagent, the blowing agent, the resol that contains already the surfaceactive agent, and a rinsing solvent are stored in storage tanks 80, 82,50 and 84, respectively, and the desired amounts of each component aretransferred, using not shown metering devices, from the tanks 80, 82 and50, through several ducts 86 connected to the feed inlet of the mixer88. The components are intimately blended in this mixer 88, and theobtained blend is transported into the casting head 90 disposed over acharging tray 91 under which an endless moving belt 94 is running; thisbelt is returned by inverting cylinders 96, 98.

The moving belt 94 is mounted on feet 100. It has for example a lengthof 15 m and a width of 80 cm, and it is driven by a variable speed motor(not shown). An extractor 93 for evacuating the gases which areexhausted by the poured mass emerging from the head 90 and having theform of a string on the moving belt, is mounted above the moving belt94; the extractor comprises a hood 97 and a fan 95 that draws in thereaction gases and send same to an air purification installation (notshown).

At the end of the moving belt, namely above the inverting cylinder 98,the string of the foamed mass is transferred onto another moving belt108 that is part of a shredder device 104, mounted on feet 102. The foamis shredded when passing between the bucket wheels 106 which are drivenin reverse direction by a motor that is not shown. The foam flakesproduced by shredding are carried away, suspended in air, by a fan 114,and they settle within a storage and conditioning chamber 116.

The operational mode of the process according to the invention willfurther be illustrated in more detail by some examples of embodiments.However, the invention will not be limited by these examples.

EXAMPLE 1

A) Resol preparation

862.5 kg of phenol, containing small amounts of water, and 20.5 kg of anaqueous solution of NaOH are charged into reactor 26 (FIG. 1). 367 kg ofparaformaldehyde are gradually introduced into this mixture within 10hours. The temperature is controlled to a value between 40° and 50° C.After the end of this introduction, stirring is continued for at least10 hours at the indicated temperature. The resol thus obtained istransferred by gravity into the ripeners 28, 30 and 32. The resol isallowed to cool to room temperature, stirring is continued for another24 hours, and the required amount of surface active agent and,optionally, of antioxidation and anti-UV stabilizers is added. Finally,the resol is transferred into the storage tank 50.

B) Preparation of a cross-linking agent

a) 220 kg of phenol are charged into reactor 52 (FIG. 2) at atemperature comprised between 40° C. and 50° C. 10 liters of sulfuricacid are slowly added under stirring, and then 45 liters of formalineare gradually introduced under stirring. Stirring is further maintainedfor 1 hour, and after abandoning during several hours, the aqueous layerthat has formed is removed by decantation. 70 liters of sulfuric acidare then added slowly and under stirring; this addition is accompaniedby an increase of the temperature. Stirring is continued for 12 hours,and the mixture of sulfonated linear phenolic oligomers that has beenobtained is transferred into the ripener-mixer 76.

b) 55 kg of phenol are charged into reactor 64 (FIG. 2), and thetemperature is raised to about 50° C. Then, 28 liters of sulfuric acidare slowly introduced under stirring. Stirring is maintained at atemperature of 60° to 75° C. during 12 hours. After cooling, 45 litersof water are slowly added into the reactor under stirring. Thesulfonated phenol thus obtained in reactor 64 is transferred into themixer 76. The cross-linking agent obtained is then transferred into thestorage tank 80.

The nature and the properties of the foam depend on the ratio betweenthe cross-linking agents a) and b).

c) It is also possible to introduce into the mixture of cross-linkingagents a) and b) a further cross-linking agent c) of the type ofsulfonated cyclic phenolic oligomers, for example belonging to the classof calixarene sulfonic acids such as the calix 6!arene p-sulfonic acid.These compounds that have never been proposed as resol cross-linkingagents yet, are for example described in the article "Synthesis andacid-base properties of calix 4!, calix 6! and calix 8!arene p-sulfonicacids" by J. P. Scharff, M. Mahjoubi and R. Perrin, New J. Chem. 1991,15, 883-887.

A preferred, combined cross-linking agent contains 2 to 4 parts ofcross-linking agent a) for 1 part of cross-linking agent b). Anotherpreferred cross-linking mixture contains from 55 to 70% of sulfonatedlinear phenolic oligomers a), from 20 to 30% of sulfonated phenol atabout 60% (dissolved in water), and from 10 to 15% of calix 6!arenep-sulfonic acid. These percentages refer to the weight.

C) Foam manufacture

Into the mixer 88 (FIG. 3A) are continuously introduced the followingamounts per minute: 7.8 kg of resol (containing 0.15 kg of surfaceactive agent), 1.2 kg of a cross-linking mixture, and 0.8 kg of blowingagent. These four components are intimately blended. The mixture ispoured through the pouring head 90 onto the moving belt 94. The pouredmass expands in a few seconds and forms a string being about 60 cm wideand 30 cm thick. The cooled string is continuously fed into the shredder104 where it is broken up into flakes that are then collected in thestoring chamber 116.

EXAMPLE 2

The following mixture (in parts by weight) is introduced into the mixerof the foam manufacturing unit:

800 parts of resol containing 16 parts of surface active agent, 150parts of cross-linking agent (a mixture of cross-linking agents a), b)and c) in a weight ratio of 62:24:13), and 80 parts of blowing agent. Afoam is formed comprising fine cells.

EXAMPLE 3

The following mixture (in parts by weight) is introduced into the mixerof the foam manufacturing unit:

800 parts of resol containing 16 parts of surface active agent, 150parts of cross-linking agent (a mixture of cross-linking agents a) andb) in a weight ratio of about 75:25), and 80 parts of blowing agent. Asmooth foam is formed comprising fine cells.

The foam thus obtained is used alike other anti-pollution products: Itis spread on the pollution site, and it rapidly absorbs the pollutingsubstances. Then, the foam that was floating, thanks to itshydrophobicity, at the surface of the aqueous medium where it has beenapplied, continues to float and may be recovered by conventional meanswhich are typically used. It has been found that the foam of theinvention can not only be manufactured at a relatively low price butshows on the other hand an extraordinary absorbing power; it has beenfound in fact during experiments that it absorbs up to 72 times itsweight of lipophilic materials.

The use of the foam is not limited to its application on aqueous media.The foam of the invention may also be used for cleaning purposes andsewage purification in industry and most specially on the floors. Thefoam may thus be transformed into different forms such as a spreadablepowder. Numerous other uses and applications are possible.

Still another application of the foam according to the invention is inthe field of hygienic and health service. This application comprises thecleaning, the filtration and the absorption in the field of common lifesuch as the recovery of frying oil, in filters of ventilator hoods, inscrubbing powders as well in absorbing terry-towels for repeated use.

For the manufacture of a phenolic plastic in the form of an absorbingfoam, a resol, a cross-linking agent as defined above, a surface activeagent and optionally a coloring agent are used according to theinvention, and it goes without saying that these constituents representthe is minimum for obtaining a desired foam. Thus, it is possible to useseveral resols, mixtures of cross-linking agents, of surface activeagents, of blowing agents, etc., or still add, if required or desired,other additives such as antioxidants, additives having an effect on themanufacturing process or the properties of the foam to be produced, andanti-UV compounds influencing the behavior of the foam in the light.

We claim:
 1. Cellular foam on the base of a phenol-formol resin,characterized in that it is constituted of a phenol formol resolcross-linked by means of a cross-linking agent selected from completelyor partially sulfonated linear and cyclic phenolic oligomers, optionallycontaining sulfonated phenol, the foam containing a surface active agentand optionally a stabilizer, and in that the foam has a hydrophobicnature permitting its use for absorbing, retaining and transportingoleophilic fatty liquids.
 2. The foam of claim 1, characterized in thatit further contains a coloring agent.
 3. The foam of claim 1,characterized in that it is in the form of flakes having a density offrom 7 to 9 kg/m³.
 4. The foam of claim 1, characterized by anabsorption power for hydrocarbons, animal and vegetable fats and otherhydrophobic pollutants up to 72 times its weight.
 5. The foam of claim1, characterized in that it is cross-linked by a cross-linking agentwhich is a mixture of completely or partially sulfonated linear phenolicoligomers and of completely or totally sulfonated phenol.
 6. The foam ofclaim 1, characterized in that it is cross-linked by a cross-linkingagent which is a mixture of completely or partially sulfonated linearand cyclic phenolic oligomers.
 7. The foam of claim 1, characterized inthat the surface active agent is an organic compound having a HLB valueof ≧10.
 8. A process for the manufacture of the foam according to claim1, characterized in that a foamable mixture is prepared starting from(A) a resol, (B) a cross-linking agent selected from completely orpartially sulfonated linear and cyclic phenolic oligomers, optionallyfurther containing sulfonated phenol, (C) a surface active agent, and(D) a blowing agent, and the mixture is poured on a support foreffecting the formation and the solidification of the foam.
 9. Theprocess of claim 8, characterized in that a coloring agent, preferablyan azoic, phenolic or calixarenic coloring agent, is added to themixture of components (A) to (D).
 10. The process of claim 8,characterized in that the cross-linking agent (B) is a mixture ofcompletely or partially sulfonated linear phenolic oligomers and ofcompletely or totally sulfonated phenol.
 11. The process of claim 8 or9, characterized in that the cross-linking agent (B) is a mixture ofcompletely or partially sulfonated linear and cyclic phenolic oligomers.12. The process of claim 8, characterized in that the surface activeagent (C) is an organic compound having a HLB value of ≧10.